296 



PHYSIOLOGY 



CHAP. 



peripheral stumps of the cervical and thoracic dorsal roots there 

 were a very few degenerated fibres, and in the central stump a 

 corresponding number of healthy fibres. But in the lumbar dorsal 

 roots more fibres were degenerated in the peripheral stump and 

 more were intact in the central stump (Fig. 179). 



Hence the degeneration method confirms this exception to the 

 Bell-Magendie law, as a few dorsal root-fibres, especially in the 

 lower lumbar segments, have a centrifugal course, and take origin 

 either from Eamon y Cajal's dorsal root cells or from the cells in 

 the ventral horn, while all the rest have their trophic centre in 

 the spinal ganglion. 



IV. Numerous physiological and clinical facts show that there 



Fiff. 179. A, transverse section of central end of 7th dorsal lumbar root of dog, showing degenera- 

 tion of most of the fibres (black discs) with very few healthy fibres. B, transverse section of 

 peripheral end of same root, showing contrary appearance. (From preparations made by 

 Tarulli and Panichi with Marchi's method.) 



is a close relation between sensation and movement, and that the 

 functions of the two spinal roots, while distinct, are not inde- 

 pendent of one another. 



The influence that the dorsal roots exercise upon the spinal 

 efferent neurones can be shown in various ways by observing the 

 reaction of the skeletal muscles. Brondgeest (1860) was the first 

 who noted relaxation or atony of the flexor muscles of the frog's 

 thigh after cutting the dorsal roots of the lumbar plexus. Harless, 

 on stimulating the frog's sciatic with a weak induction current, 

 before and after section of the same roots, found the constant 

 effect of division to be diminished excitability in the nerve. 



Cyon (1865) first experimented directly on the spinal roots, 

 and demonstrated that the integrity of the dorsal roots is indis- 

 pensable to the normal excitability of the corresponding ventral 

 roots. Section of the former produces a depression of excitability 

 in the latter. 



